Firm A operates in perfect competition, firm B in monopolistic competition and firm C is a monopoly. Which of the following statements on A, B and C does not hold? Select one: O a. Over the long run, A makes no profit, C generates a welfare loss and B does both O b. Marginal revenue is equal to the price of the good for A, not for B nor C O c. A, B and C can all make profit over the short run O d. For profit maximization, marginal cost equals marginal revenue for B and C, but not for A